Various methods and devices are available for analysing materials.
The selection of a particular method or device depends on, amongst other requirements, the quantity of the material that may be analysed in a given time.
For example, transmission electron microscopy (TEM) is a valuable tool in materials characterization, but sample analysis is a slow process. Typically, samples of the material must be prepared thin enough to be electron beam transparent. Although a high degree of information may be obtained by TEM analysis, the number of samples that can be prepared and analysed in a single day is very limited. Additionally, the cost of TEM analysis is prohibitive.
High through-put analysis methods and devices are required where large volumes of materials need to be characterized. An example of such an application is waste recycling where glass, for example, needs to be differentiated from metals and plastics.
Another example involves characterizing mined materials. In this regard, one method of analysing particles of as-mined material is disclosed in U.S. Pat. No. 3,655,964 to Slight.
The method involves passing as-mined material through a field of x-radiation at two energy levels in a gap between an x-radiation generating source and a series of x-radiation detectors and determining the intensity of x-radiation that is transmitted through the mined material.
Data on the intensity of transmitted x-radiation at one energy level is obtained at the detectors and is used, in conjunction with a known x-radiation absorption coefficient for a known material, to determine a nominal thickness for the known material. The determined thickness is then used, in conjunction with data obtained at the detectors of transmitted x-radiation at the other energy level, to calculate an x-ray absorption coefficient for the ore. The calculated coefficient is compared against the known coefficient of the known material at the other energy level. If the calculated x-radiation absorption coefficient corresponds with the known coefficient for the known material, the mined material is identified as the known material. If the calculated x-radiation absorption coefficient does not correspond with the known coefficient for the known material, the process is repeated with alternative x-radiation absorption coefficients for other known materials until a match is found.
The claimed advantage of this approach is that the thickness of a particle is removed from consideration in characterizing the material.
The applicant has recognized that the problem with this approach is that the method disclosed in Slight is limited and in practice impossible to implement. Specifically:    1. Slight assumes mono-energy x-radiation beams which in practice are not available or possible, and ignores the impacts of beam hardening and beam scattering which make an accurate assessment of characterization not possible.    2. Use of a pulse height analyser is not possible to operate on particles passing the detector counter at speeds of greater than 1 m/s. Hence, this greatly limits the through-put capacity of the method.    3. The embodied designs of pulsing energy levels from a single energy source, sequentially positioned energy sources or sequentially positioned detection counters do not ensure the same section and orientation of a particle is analysed at each energy level. This introduces analysis errors, and is particularly evident in high speed/high through-put applications as changes in particle position, orientation and trajectory are more pronounced.
In addition, the applicant has recognized that Slight does not disclose how the concentration of constituents of the material can be determined from the analysis method disclosed by Slight.
It is an object of the invention to provide an improved method of analysing materials.